U.S. patent number 6,690,172 [Application Number 10/009,395] was granted by the patent office on 2004-02-10 for multiple electric conductivity measuring apparatus.
This patent grant is currently assigned to Organo Corporation. Invention is credited to Yuji Higo.
United States Patent |
6,690,172 |
Higo |
February 10, 2004 |
Multiple electric conductivity measuring apparatus
Abstract
A multiple electric conductivity measuring apparatus having at
least two electric conductivity measuring cells each having at
least two electrodes brought into contact with a substance to be
measured, wherein the electric conductivity measuring cells are so
connected electrically that the sensing signals therefrom can be
added and/or subtracted. The measuring apparatus can measure a
micro difference or variation of the electric conductivity between
a plurality of measuring points different in position or time with
high reliability, accuracy and sensitivity.
Inventors: |
Higo; Yuji (Tokyo,
JP) |
Assignee: |
Organo Corporation (Tokyo,
JP)
|
Family
ID: |
18567969 |
Appl.
No.: |
10/009,395 |
Filed: |
October 22, 2001 |
PCT
Filed: |
February 15, 2001 |
PCT No.: |
PCT/JP01/01073 |
PCT
Pub. No.: |
WO01/63268 |
PCT
Pub. Date: |
August 30, 2001 |
Foreign Application Priority Data
|
|
|
|
|
Feb 23, 2000 [JP] |
|
|
2000-45374 |
|
Current U.S.
Class: |
324/439; 324/450;
324/691 |
Current CPC
Class: |
G01N
27/06 (20130101); G01N 27/07 (20130101) |
Current International
Class: |
G01N
27/06 (20060101); G01N 27/07 (20060101); G01R
027/22 () |
Field of
Search: |
;324/439,442,444,450,687,654,688,691 ;73/862.628,61.21 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Le; N.
Assistant Examiner: Nguyen; Vincent Q.
Attorney, Agent or Firm: Norris McLaughlin & Marcus
Parent Case Text
This application is a 371 of PCT/JP01/01073 filed on Feb. 15, 2001.
Claims
What is claimed is:
1. A multiple electric conductivity apparatus comprising at least
two electric conductivity measuring cells each having at least two
electrodes brought into contact with a substance to be measured,
said electric conductivity measuring cells being so connected
electrically that sensing signals themselves from said electric
conductivity measuring cells are treated to be added and/or
subtracted, said at least two electrodes of each of said at least
two electric conductivity measuring cells being constructed so that
their electrode surfaces are formed by titanium oxide layers on
surfaces of electrode bodies made of a conductive material, wherein
each electric conductivity measuring cell has a space for storing a
substance to be measured which is defined between respective
electrode surfaces of said at least two electrodes, and light
irradiating means for irradiating light onto the respective
electrode surfaces, and wherein said light irradiating means
comprises a light guiding material which guides light from a light
source.
2. A multiple electric conductivity apparatus comprising at least
two electric conductivity measuring cells each having at least two
electrodes brought into contact with a substance to be measured,
said electric conductivity measuring cells being so connected
electrically that sensing signals themselves from said electric
conductivity measuring cells are treated to be added and/or
subtracted, said at least two electrodes of each of said at least
two electric conductivity measuring cells being constructed so that
their electrode surfaces are formed by titanium oxide layers on
surfaces of electrode bodies made of a conductive material, wherein
each electric conductivity measuring cell has a space for storing a
substance to be measured which is defined between respective
electrode surfaces of said at least two electrodes, and light
irradiating means for irradiating light onto the respective
electrode surfaces, and wherein said space for storing a substance
to be measured is defined by a light transmitting material, and
light from said light irradiating means is irradiated onto said
electrode surfaces through said light transmitting material.
3. The multiple electric conductivity measuring apparatus according
to claim 2, wherein a titanium oxide coating layer capable of
transmitting light is provided on a surface of said light
transmitting material of its side facing said space for storing a
substance to be measured.
Description
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a multiple electric conductivity
measuring apparatus having a plurality of electric conductivity
measuring cells, and more specifically, relates to a multiple
electric conductivity measuring apparatus capable of accurately
measuring a difference or variation of the electric conductivities
between measuring points different in position or time in a
treatment system containing a substance to be measured such as an
aqueous solution and the like.
BACKGROUND ART OF THE INVENTION
Electric conductivity is especially employed as a scale to measure
a concentration of ions capable of migrating in an aqueous
solution, and an electric conductivity measuring apparatus is used
to measure ion concentrations in many kinds of aqueous solutions.
An electric conductivity measuring apparatus, generally, determines
an increase or a decrease of the ion concentration of an aqueous
solution to be measured by measuring the resistance of the aqueous
solution existing between an electric conductivity detection
electrode and an electric current supply electrode connected to a
power source.
As a method for using a conventional electric conductivity
measuring apparatus, the electric conductivity measuring apparatus
is installed at a predetermined measuring point, or a sample
solution is introduced from a predetermined measuring point into
the electric conductivity measuring apparatus, and the electric
conductivity measured by the apparatus is utilized for observing
the condition of an aqueous solution or controlling the water
quality thereof and the like in many kinds of fields. In the
measurement of electric conductivity by the electric conductivity
measuring apparatus, usually, the measurement is conducted after
adjusting the measuring range of the electric conductivity
measuring apparatus in accordance with a condition of a substance
to be measured, a condition of an electrode, a condition of the
circumstances at the time of the measurement (for example, an
ambient temperature or a condition of noises from surrounding
equipment) and the like. Further, in this measurement, a surface
condition of the electrode often varies with time since organic
substances and the like contained in a substance to be measured
onto the electrode of the electric conductivity measuring
apparatus. In such a condition, a drift from a desired measuring
standard point occurs more or less during the measurement.
Therefore, the data of the electric conductivity measured by the
electric conductivity measuring apparatus are deemed to be data
which are relatively low in reliability as data used for operation
management or control, and it is the present situation that the
data are considered as secondary data.
Especially, in a case where measurement data of electric
conductivity are collected from a plurality of measuring points,
and, for example, a progress degree of a treatment of an aqueous
solution between the plural measuring points, or a variation of
water quality between these measurement points, and further, in a
case where a variation of the electric conductivity with time is
measured at a substantially identical measuring position,
practically it is difficult to measure with a high accuracy,
because the measuring range of each apparatus is adjusted, or a
drift occurs with time, as described above. Further, when a
variation of electric conductivity, or a difference in electric
conductivities between a plurality of measuring points is to be
measured, in a case where the variation or the difference is much
smaller than the absolute value of the electric conductivity which
is being measured, since the measuring range is adjusted relative
to the relatively great absolute value of the electric
conductivity, it is very difficult to distinguish such a micro
variation or difference, or, the measured data become low in
reliability. In practice, however, there are many requirements to
measure such a micro difference or variation between two or a
plurality of measuring points different in position or time. If
such a micro difference or variation can be measured with a high
reliability, a high accuracy and a high sensitivity, it is
considered that the use is very broad. However, an electric
conductivity measuring apparatus capable of satisfying such
requirements has not yet been found.
DISCLOSURE OF THE INVENTION
Accordingly, it is an object of the present invention to provide a
multiple electric conductivity measuring apparatus capable of
measuring a micro difference or variation of electric conductivity
between a plurality of measuring points different in position or
time with a high reliability, a high accuracy and a high
sensitivity to satisfy the above-described requirements.
To accomplish the above-described object, a multiple electric
conductivity measuring apparatus according to the present invention
comprises at least two electric conductivity measuring cells each
having at least two electrodes brought into contact with a
substance to be measured, the electric conductivity measuring cells
are so connected electrically that sensing signals themselves from
the electric conductivity measuring cells can be treated to be
added and/or subtracted.
Namely, in a conventional electric conductivity measuring
apparatus, a sensing signal from one electric conductivity
measuring cell is amplified by an amplifier and the like, and the
amplified signal is rectified into a signal with an appropriate
level as an output signal for measuring an electric conductivity,
and when a plurality of electric conductivity measuring apparatuses
are installed, it has been necessary to adjust a measuring range
for each electric conductivity measuring apparatus. In the multiple
electric conductivity measuring apparatus according to the present
invention, however, within the apparatus itself, an electrical
calculation treatment such as addition, subtraction and the like is
performed with respect to the sensing signals themselves sent from
the respective electric conductivity measuring cells, and the
signal after the treatment is amplified as needed, and is output as
a difference or variation between the electric conductivities
measured at the respective electric conductivity measuring cells.
Therefore, the multiple electric conductivity measuring apparatus
according to the present invention is basically and distinctly
different from the conventional technology in that the conventional
electric conductivity measuring apparatuses are merely disposed in
plural form and a difference or variation between the data measured
by the apparatuses is obtained.
In this multiple electric conductivity measuring apparatus
according to the present invention, the above-described at least
two electrodes in each electric conductivity measuring cell can be
constructed from an electric conductivity detection electrode and
an electric current supply electrode. The two-electrode formation
itself as the constitution of the electrode is heretofore known. To
the electric current supply electrode, for example, an AC current
is supplied. In a case where a plurality of electric current supply
electrodes are disposed, an amplified or attenuated AC current may
be supplied to at least one electric current supply electrode. If
an AC current is amplified before being supplied to an electric
current supply electrode, it can create substantially the same
condition that the supplied electric current is multiplied by a
predetermined magnification, and the same effect of the
multiplication can be obtained also on sensing signals sent from
the electric conductivity measuring cells. If an AC current is
attenuated before being supplied to an electric current supply
electrode, it can create substantially the same condition that the
supplied electric current is divided by a predetermined rate, and
the same effect of the division can be obtained also on sensing
signals sent from the electric conductivity measuring cells. If the
sensing signals themselves thus created are added or subtracted,
the multiplication or the division is included in the addition or
the subtraction, and, when the sensing signals themselves are
treated, as needed, it also becomes possible that addition,
subtraction, multiplication and division are combined arbitrarily.
The signal created after treating the sensing signals themselves
sent from the electric conductivity measuring cells as described
above can be amplified in order to optimize the level of the output
signal, as needed, and in such a case, because an object is the
single signal after the treatment, a single amplifier may be
provided.
Further, in the multiple electric conductivity measuring apparatus
according to the present invention, it may be constituted that each
of the electric conductivity measuring cells has three electrodes,
the three electrodes include an electric conductivity detection
electrode and two AC current supply electrodes disposed on both
sides of the electric conductivity detection electrode at
respective distances, and an AC current of the same phase is
applied to the two AC current supply electrodes. Alternatively, it
may be constituted that each of the electric conductivity measuring
cells has three electrodes, the three electrodes include an
electric conductivity detection electrode, an AC current supply
electrode disposed on one side of the electric conductivity
detection electrode at a distance, and a grounded electrode
disposed on the other side of the electric conductivity detection
electrode at a distance. By such three-electrode constitutions, a
high-accuracy measurement, free from adverse effects from
circumstances such as noises, becomes possible, as described
later.
Further, in the multiple electric conductivity measuring apparatus
according to the present invention, it is preferred that the
above-described at least two electrodes in each electric
conductivity measuring cell are constructed so that their electrode
surfaces are formed by titanium oxide layers on surfaces of
electrode bodies made of a conductive metal. In such a
constitution, when organic substances and the like are contained in
a substance to be measured, the property for decomposing organic
substances based on the photocatalytic activity of the titanium
oxide, and its super-hydrophilicity can be effectively utilized, in
order to eliminate adverse effects on the measurement of the
electric conductivity due to the adhesion or adsorption of the
organic substances to the electrode surfaces. It is preferred that
light irradiating means is disposed against the titanium oxide
layers to provide a photocatalytic activity to the titanium oxide
layers. For example, each electric conductivity measuring cell can
be constructed so as to have a space for storing a substance to be
measured defined between respective electrode surfaces of the
above-described at least two electrodes, and light irradiating
means that irradiates light onto the respective electrode
surfaces.
In this multiple electric conductivity measuring apparatus, it is
preferred that light irradiated by the above-described light
irradiating means has a wavelength which brings about a
photocatalytic activity of the above-described titanium oxide
layers. For example, light with a wavelength from about 300 to
about 400 nm can be employed. As the light irradiating means, a
light source composed of means for irradiating ultraviolet rays and
the like such as a black light may be directly employed, and a
light guiding material (for example, an optical fiber, or tube and
the like comprising a light guiding raw material) to guide light
from a light source provided as means for irradiating light may
also be employed. Further, the light from a light guiding material
may be added to light irradiated directly from a light source.
Further, the above-described space for storing a substance to be
measured may be defined by a light transmitting material, and it
may be constituted so that the light from the light irradiating
means is irradiated onto an electrode surface through the light
transmitting material (for example, glass). In this case, if a
titanium oxide coating layer capable of transmitting light is
provided on the surface of the light transmitting material at its
side facing the space for storing a substance to be measured (a
surface in contact with solution), adhesion of organic substances
and the like to this surface of the light transmitting material can
be prevented by super-hydrophilicity and organics decomposition
property ascribed to the titanium oxide layer.
Further, the above-described electrode can be produced by, for
example, the following method. Namely, a method can be employed
wherein an electrode surface is formed by providing on a titanium
oxide layer on a surface of an electrode body made of a conductive
metal by a surface treatment such as sputtering, plating or the
like. Alternatively, a method can also be employed wherein an
electrode surface made of a titanium oxide layer is formed by
providing oxygen to a surface of an electrode body made of
titanium. As the method for forming a titanium oxide layer by
providing oxygen, a method based on air oxidation other than a
method utilizing electrolysis can be employed.
In the multiple electric conductivity measuring apparatus according
to the present invention as described above, a treatment of at
least either addition or subtraction is added to the sensing
signals themselves sent from the respective electric conductivity
measuring cells in the apparatus, and the signal created after the
treatment is output as a single sensing signal. A treatment such as
amplification and the like is added to this sensing signal, as
needed. The sensing signal thus output corresponds to a difference
between the detected electric conductivities at positions set with
the respective electric conductivity measuring cells, or a
variation between the detected electric conductivities at positions
set with the respective electric conductivity measuring cells. It
is possible that both of the detected electric conductivities are
measured at a substantially same condition or same measuring range,
it is not necessary to adjust this condition or measuring range to
be met with the scale of the absolute value of the electric
conductivity, and it may be adjusted depending on the scale of the
above-described difference or variation. Therefore, even when the
above-described difference or variation is fine relatively to the
scale of the absolute value of the electric conductivity, the micro
difference or variation can be extracted with a high accuracy and a
high sensitivity. Besides, as described above, since the sensing
signals themselves from the respective electric conductivity
measuring cells when electrically calculating the difference or
variation are signals extracted at a substantially same adjustment
condition within a single apparatus, a difference in effect due to
the adjustment of the measuring range and the like is not generated
between the sensing signals themselves from the respective electric
conductivity measuring cells which are the sources of the
calculation. Therefore, also from this point of view, it is
guaranteed that the above-described difference or variation is
extracted accurately, and it can ensure very highly reliable
data.
Thus, in the multiple electric conductivity measuring apparatus
according to the present invention, since sensing signals
themselves from the respective electric conductivity measuring
cells can be treated to be at least added and/or subtracted, the
measuring apparatus can measure a micro difference or variation of
the electric conductivity between a plurality of measuring points
different in position or time with a high accuracy and a high
sensitivity, and an extremely high-reliability data can be obtained
with respect to the measurement of electric conductivity.
BRIEF EXPLANATION OF THE DRAWINGS
FIG. 1 is an electric circuit diagram of a multiple electric
conductivity measuring apparatus according to an embodiment of the
present invention.
FIG. 2 is an electric circuit diagram of a multiple electric
conductivity measuring apparatus according to another embodiment of
the present invention.
FIG. 3 is a schematic view of a water treatment system which
incorporates a multiple electric conductivity measuring apparatus
according to the present invention.
FIG. 4 is an electric circuit diagram showing an example of a
multiple electric conductivity measuring apparatus according to the
present invention usable for conductivity measurement in the water
treatment system depicted in FIG. 3.
FIG. 5 is a schematic view showing an example of a multiple
electric conductivity measuring apparatus according to the present
invention in which a time delay column is used.
FIG. 6 is a schematic diagram showing an example of an electric
conductivity measuring cell usable for a multiple electric
conductivity measuring apparatus according to the present
invention.
FIG. 7 is a schematic diagram showing another example of an
electric conductivity measuring cell usable for a multiple electric
conductivity measuring apparatus according to the present
invention.
FIG. 8 is a schematic diagram showing a further example of an
electric conductivity measuring cell usable for a multiple electric
conductivity measuring apparatus according to the present
invention.
FIG. 9 is an exploded perspective view showing an example of the
mechanical constitution of an electric conductivity measuring cell
usable for a multiple electric conductivity measuring apparatus
according to the present invention.
FIG. 10 is a perspective view showing an example of the
constitution of an electrode of an electric conductivity measuring
cell usable for a multiple electric conductivity measuring
apparatus according to the present invention.
FIG. 11 is an exploded perspective view showing another example of
the mechanical constitution of an electric conductivity measuring
cell usable for a multiple electric conductivity measuring
apparatus according to the present invention.
THE BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, preferred embodiments of the present invention will be
explained referring to Figures.
FIG. 1 shows an electric circuit constitution of a multiple
electric conductivity measuring apparatus according to an
embodiment of the present invention. In FIG. 1, a multiple electric
conductivity measuring apparatus 1 has at least two electric
conductivity measuring cells (in this embodiment, a two-cell
constitution is depicted) each having at least two electrodes (in
this embodiment, a three-electrode constitution is depicted)
brought into contact with a substance to be measured. In this
embodiment, the electric conductivity measuring cells 2, 3 (FIG. 1
indicates them as "cell 1" and "cell 2", respectively) are
connected electrically so that sensing signals themselves from the
electric conductivity measuring cells 2, 3 can be treated to be
added.
The electric conductivity measuring cells 2, 3 are connected
electrically in parallel with each other, and an AC current with
the same phase is supplied from an AC oscillator 4 provided as a
power source to electric current supply electrodes 2a, 3a of the
respective electric conductivity measuring cells 2, 3. The electric
conductivity detection electrodes 2b, 3b of the respective electric
conductivity measuring cells 2, 3 are electrically connected to
each other, and the detection signals themselves from the electric
conductivity detection electrodes 2b, 3b can be added. In this
embodiment, a multiplication unit or division unit 5 for
multiplying the value of AC current to be supplied at a
predetermined magnification or for dividing it with a predetermined
rate is provided before the electric conductivity detection
electrode 2a of the electric conductivity measuring cell 2, and the
level of an electric conductivity of a substance to be measured as
an object detected by the electric conductivity measuring cell 2 is
made different from that by the electric conductivity measuring
cell 3. Namely, an AC current before being supplied to the electric
current supply electrode 2a is amplified or attenuated at a
predetermined magnification. By this, as described later, in a
treatment system, the respective electric conductivities can be
detected at optimized sensitivities with respect to the respective
detecting positions before the treatment and after the treatment
(for example, after concentration or after dilution).
The signal obtained after the above-described treatment of the
electric calculation, namely, the signal obtained from a coupled
point of the electric conductivity detection electrodes 2a, 3a, is
amplified to an appropriate level suitable as an output signal, by
a single amplifier 6. At this juncture, an optimum measuring range
can be selected depending upon the measurement object by a
measuring range switching unit 7.
In this embodiment, the signal sent from amplifier 6 is
synchronized with the output side of the AC current oscillator 4 by
a synchronous rectifier 9, after a temperature compensation for the
measurement environment is performed by a temperature compensator
8. Further, the signal is amplified by an amplifier 11 with a range
controller 10 so as to become a signal with an optimum level for a
certain kind of control or display of output, and it is extracted
as an actual output 12.
FIG. 2 shows an electric circuit of a multiple electric
conductivity measuring apparatus according to another embodiment of
the present invention. In a multiple electric conductivity
measuring apparatus 21 according to this embodiment, as compared
with the embodiment shown in FIG. 1, a multiplication unit or
division unit 22 for multiplying AC current to be supplied at a
predetermined magnification or for dividing it with a predetermined
rate is provided before the electric conductivity detection
electrode 3a of the electric conductivity measuring cell 3, and the
level of an electric conductivity of a substance to be measured as
an object detected by the electric conductivity measuring cell 3 is
made different from that by the electric conductivity measuring
cell 2. A phase reversing function is provided to this
multiplication unit or division unit 22. Namely, AC current before
being supplied to the electric current supply electrode 3a is
amplified or attenuated at a predetermined magnification, and at
the same time, the phase of the supplied AC current is reversed. By
this, the sensing signals themselves from the respective electric
conductivity measuring cells 2, 3 are substantially subtracted, and
the signal treated by the subtraction is sent to the amplifier 6.
Other constitutions are the same as those shown in FIG. 1.
The multiple electric conductivity measuring apparatus constructed
as described above is used, for example, as shown in FIG. 3. FIG. 3
shows a water treatment system 31, the system has a tank 33 for
storing concentrated or diluted water (for example, a cooling
tower, a dilution reservoir and the like) against raw water 32. The
stored water 34 is sent by a pump 35 from the tank 33 to a next
treatment system or operation system. In such a water treatment
system 31, when measured is a difference of electric conductivity
or a variation of electric conductivity between the raw water 32
and the concentrated or diluted water in the tank 33 (hereinafter,
referred to as concentrated water and the like 34) is to be
measured as shown in FIG. 3, the raw water 32 and the concentrated
water and the like 34 are taken out as sample waters through a
degasifier 36. Sampled raw water 32 and concentrated water and the
like 34 are sent to electric conductivity measuring cells 39, 40
(which correspond to the aforementioned electric conductivity
measuring cells 2, 3 channel 1 (ch1), channel 2 (ch2)),
respectively, and the electric conductivities are measured. The
waters after measurement are discharged, or returned to an
appropriate recycle system.
In this case, although the sensing signals sent from the respective
electric conductivity measuring cells 39, 40 can be extracted as
absolute values of the electric conductivities of the raw water 32
and the concentrated water and the like 34, respectively, in the
present invention, mainly sensing signals (output 1, output 2 in
the Figure) detected by the electric conductivity measuring cells
39, 40 receive the treatment of the electric calculation as
aforementioned, and the treated signal is detected as a difference
or variation of electric conductivities at the both detecting
positions.
In the detection system shown in FIG. 3, a multiple electric
conductivity measuring apparatus 41 as shown in FIG. 4, for
example, is constituted. In the multiple electric conductivity
measuring apparatus shown in FIG. 4, an AC current from an AC
oscillator 42 is supplied to the respective electric conductivity
measuring cells 39, 40. An AC current, which is amplified by a
phase reversing amplifier 44 with a magnification setting unit 43
at a predetermined magnification and the phase of which is
reversed, is supplied to one electric conductivity measuring cell
39. To the other electric conductivity measuring cell 40, an AC
current amplified at a constant magnification by an amplifier 45 is
supplied without reversing its phase. The output sides of the
respective electric conductivity measuring cells 39, 40 are
connected to each other, and since the phase of the above-described
one supplied AC current is reversed, a subtraction treatment is
conducted to create a difference between the sensing signals sent
from both of the electric conductivity measuring cells 39, 40. This
subtraction treated signal is amplified by an amplifier 47 with a
sensitivity (measuring range) switching unit 46, and output as a
single output signal 48. Therefore, this output signal 48 indicates
a difference or variation between the detected electric
conductivities of both of the electric conductivity measuring cells
39, 40.
Thus, since the difference or the variation is not calculated from
the absolute values of the sensing signals output from the
respective electric conductivity measuring apparatuses, but the
subtraction treatment is performed with respect to the sensing
signals themselves from the respective electric conductivity
measuring cells 39, 40 in a single multiple electric conductivity
measuring apparatus 41, only the difference or variation between
electric conductivities of both of the electric conductivity
measuring cells 39, 40 can be extracted accurately. Further,
because the measuring range at the time of this measurement may be
adjusted not relative to the absolute value of electric
conductivity but relative to the difference or variation of
electric conductivity to be detected, even if the difference or
variation is much smaller than the absolute value of electric
conductivity, the adjustment to an optimum measuring range
regardless to the absolute value of electric conductivity is
possible, and an extremely high-accuracy and high-sensitivity
measurement becomes possible.
Further, since the level of the current supplied to one electric
conductivity measuring cell 39 can be appropriately switched by the
magnification switching unit 43, an optimum adjustment of
sensitivity can be performed for any of a concentration system or a
dilution system. Moreover, since the sensitivity (measuring range)
switching unit 46 is provided also on the output side, the level of
the signal finally output can also be adjusted to an optimum level,
and the data of the difference or variation of electric
conductivity can be determined at an optimum sensitivity. As a
result, extremely high-reliability data of the difference or
variation in the electric conductivity measurement can be obtained
with a high accuracy and a high sensitivity.
In the measurement system shown in FIG. 3, although the difference
or variation of the electric conductivity measurement between
different two positions sandwiching a water treatment system is
measured, in the present invention a variation with time of the
electric conductivity measurement in a flow direction of a
substance, for example, can be measured.
For example, as shown in FIG. 5, when a variation of electric
conductivity measurement between different positions is measured in
the flow direction of the water flowing in a water flow tube 52, a
multiple electric conductivity measuring apparatus 51 is disposed
to take out a sample water through, for example, a Venturi tube 54
at an upstream position 53. After the electric conductivity of this
sample water is at first detected by one electric conductivity
measuring cell 55, the sample water is sent to the other electric
conductivity measuring cell 57 through a time delay column 56, the
electric conductivity of the sample water is measured again in this
cell 57, and the sample water after the measurement is returned to
a downstream position 58 of the water flow tube 52. The time delay
column 56 is designed to adjust a residual time from an end of
inlet to an end of outlet by, for example, winding a capillary
spirally, and in this embodiment, the residual time is adjusted to
substantially correspond to a flow time from the upstream position
53 to the downstream position 58 of the water flow tube 52.
By providing such time delay column 56 and timely shifting the
timing of electric conductivity detection as to an identical sample
water, it can be observed how the electric conductivity varies
between these two different times. And, by employing the multiple
electric conductivity measuring apparatus 51 according to the
present invention for this observation, the variation of electric
conductivity is detected with a high reliability, a high accuracy
and a high sensitivity.
In the present invention, the structures of the respective electric
conductivity measuring cells are not particularly restricted, and
they may be each constructed to have at least two electrodes
brought into contact with a substance to be measured. In the case
where two electrodes are used in each electric conductivity
measuring cell, one is an electric conductivity detection electrode
and the other is an electric current supply electrode, and when
three-electrode constitution is employed, one of the three
electrodes can be formed as a grounded electrode. Although it is
preferred that an AC current is supplied to the electric current
supply electrode, a constitution for supplying a DC current can
also be employed.
FIG. 6 shows a schematic constitution of an electric conductivity
measuring cell having a two-electrode formation applicable to the
present invention. In the electric conductivity measuring cell 61
shown in FIG. 6, a power supply electrode 64 and an electric
conductivity detection electrode 65 are disposed at a distance in a
fluid 63 to be measured and flowing in a measurement tube 62 or
being stored in the tube 62. An AC current is applied to the power
supply electrode 64 from, for example, a power source (not shown)
through an amplifier 66, and a detection current from the electric
conductivity detection electrode 65 receives the treatment of the
aforementioned addition or subtraction.
In the electric conductivity measuring cell 61 of two-electrode
formation as described above, the measuring tube 62 is composed of
an insulation material (for example, a vinyl chloride tube) at
least at the position of the above-described electric conductivity
measurement, since the system is often substantially in a grounded
condition at any position of the extending portion of the tube,
noises may be picked up from the environment, originating from the
grounded condition.
In order to remove any effect ascribed to such noises, it is
preferred that electric conductivity measuring cells having
three-electrode constitutions, for example, as shown in FIGS. 7 and
8, are used. In an electric conductivity measuring cell 71 shown in
FIG. 7, three electrodes 74, 75, 76 brought into contact with a
fluid 73 to be measured are provided in the fluid 73 to be measured
and flowing in an insulated measuring tube 72 or being stored in
the measuring tube 72. The three electrodes comprise an electric
conductivity detection electrode 74 for detecting electric
conductivity and two AC current supply electrodes 75, 76 disposed
on both sides of the electric conductivity detection electrode 74
at respective distances. AC current of the same phase is applied
with a constant voltage and the same potential to the two AC
current supply electrodes 75, 76 through an amplifier 77. The
detected current from the electric conductivity detection electrode
74 receives the treatment of the aforementioned addition or
subtraction.
In the electric conductivity measuring cell 71 shown in FIG. 7, the
electric conductivity measuring electrode 74 is electrically
shielded against a grounded point which would exist at any point of
the extending portion of the measurement tube 72 by the two AC
current supply electrodes 75, 76, which are disposed on both sides
of the electric conductivity detection electrode 74, and to which
an AC current of the same phase is supplied. Namely, since a
constant voltage AC current with the same phase is applied to the
two AC current supply electrodes 75, 76, and the potential
difference between the electric conductivity detection electrode 74
and the AC current supply electrode 75, 76 is always maintained at
a predetermined constant value, substantially no electric
resistance exists between the electric conductivity detection
electrode 74 and an outside grounded point. Therefore, any
resistance between an electric conductivity detection electrode and
an outside grounded point, and any influence on an output electric
current from the electric conductivity detection electrode
originating from a variation of any such resistance, as in the cell
constitution shown in FIG. 6, disappear substantially completely.
In other words, any leaked electric current from the electric
conductivity detection electrode 74 to the outside grounded point
does not exist at all. As a result, the output electric current
from the electric conductivity detection electrode 74 is extracted
at a condition with no disturbance at all times, and dispersion and
variation due to the disturbance are prevented, thereby ensuring a
stable and high-accuracy measurement of electric conductivity at
all times.
In the electric conductivity measuring cell 81 shown in FIG. 8,
three electrodes 84, 85, 86 brought into contact with a fluid 83 to
be measured are provided in the fluid 83 flowing in an insulated
measurement tube 82 or being stored in the measurement tube 82. The
three electrodes comprise an electric conductivity detection
electrode 84 for detecting electric conductivity and an AC current
supply electrode 85 disposed on one side of the electric
conductivity detection electrode 84 at a distance, and a grounded
electrode 86 disposed on the other side of said electric
conductivity detection electrode 84 at a distance. An AC current
with the phase is applied at a constant voltage to the AC current
supply electrodes 85 through an amplifier 87. The detected current
from the electric conductivity detection electrode 84 receives the
treatment of the aforementioned addition or subtraction.
In the electric conductivity measuring cell 81 shown in FIG. 8, an
AC current with a constant voltage is supplied only to the AC
current supply electrode 85, the grounded electrode 86 is forcibly
made to be zero in potential by the grounding, and these electrodes
85, 86 are disposed on both sides of the electric conductivity
detection electrode 84. Therefore, the portion between the
electrodes 85, 86 is divided in electrical circuit in a formation
of a so-called resistive division, by the electric conductivity
detection electrode 84. In the circuit between these electrodes 85,
86, a predetermined AC current with a constant voltage is applied
to the electrode 85, and the potential of the electrode 85 is
always forced to be zero, and this condition is always maintained
stably. Namely, even if any extending portion of the measurement
tube 82 is grounded, there is no room to allow a resistance to
enter between the grounded point and the electric conductivity
detection electrode 84, thereby preventing the electric current
extracted from the electric conductivity detection electrode 84
from shifting or varying. Therefore, the output electric current
from the electric conductivity detection electrode 84 is extracted
at a condition with no disturbance at all times, and dispersion and
variation due to the disturbance are prevented, thereby ensuring a
stable and high-accuracy measurement of electric conductivity at
all times.
In the present invention, the mechanical construction of an
electric conductivity measuring cell is not particularly
restricted, and it can be formed as a construction shown in FIG. 9
for example. In the electric conductivity measuring cell 91 shown
in FIG. 9, an electric conductivity measuring electrode 94 shown in
FIG. 10 is preferably used for example, wherein an electrode
surface is formed by a titanium oxide layer 93 on the surface of an
electrode body 92 made of a conductive metal. The titanium oxide
layer 93 is formed by a surface treatment such as sputtering,
plating and the like, or is formed by oxidizing the surface of the
electrode body 92 made of a titanium metal. The oxidation is
conducted by electrolysis or air oxidation.
The electric conductivity measuring electrodes 94 are used as
electrodes corresponding to two or three electrodes shown in FIGS.
6 to 8, and are attached to an electrode holder 95 made of an
insulation material in a condition where the electrode surfaces are
exposed as shown in FIG. 9. Three electrodes 94 are disposed in a
raw, and the electrodes 94a and 94b at both sides constitute AC
current supply electrodes connected to a power source, and the
electrode 94c at the central position constitutes an detection
electrode functioning as a sensor for detecting electric
conductivity.
Electrode holder 95 is fixed at a predetermined position of a
substrate 96. In the substrate 96, inlet 97 for introducing a fluid
to be measured (for example, an aqueous solution), outlet 98 for
discharging the fluid, and flow holes 99 and 100 for measuring
electric conductivity are provided. In the electrode holder 95,
flow holes 101 and 102 are provided, and the flow hole 101 is
disposed to communicate with the flow hole 99 of the substrate, and
the flow hole 102 is disposed to communicate with flow hole 100 of
the substrate, respectively. A fluid to be measured introduced from
inlet 97 is sent into a space 104 for storing a substance to be
measured, which is defined on the side of the electrode surfaces of
the respective electrodes 94 through an inside path 103 of the
substrate 96, the flow hole 99, and the flow hole 101 of electrode
holder 95. The space 104 for storing a substance to be measured
forms a flow path for measuring electric conductivity of a fluid to
be measured. The fluid from the space 104 for storing a substance
to be measured is discharged from outlet 98 through the flow hole
102 of electrode holder 95, the flow hole 100 of the substrate 96,
and an inside path 105.
In the substrate 96, through holes 106a, 106b, 106c are opened at
positions corresponding to the respective electrodes 94a, 94b, 94c,
and necessary electric wires are pulled out of the through holes
106a, 106b, 106c.
The space 104 for storing a substance to be measured, in this
embodiment, is defined by a sheet-like packing 107, and a
transparent glass plate 108 provided as a light transmitting
material which is disposed to confront electrode holder 95 with a
gap via packing 107. It is preferred that a titanium oxide coating
layer is provided to such an extent that the light transmitting
property is not damaged, also to the surface of glass plate 108 on
its side facing the space 104 for storing a substance to be
measured. The electric conductivity of the fluid, flowing in this
space 104 for storing a substance to be measured, is measured.
Electrode holder 95, packing 107 and glass plate 108 are fixed to a
cover body 110 on one surface side of substrate 96 by bolts 109. A
window 111 for transmitting light is opened on cover body 110.
Through this window 111, light from light irradiating means 112
which is disposed outside is irradiated. Light irradiated is shed
on titanium oxide layers 93 that form the electrode surfaces of the
respective electrodes 94a, 94b, 94c through glass plate 108 from
the window 111. Light having a wavelength that brings about a
photocatalytic activity of titanium oxide layers 93 is selected as
the light to be irradiated. For example, an ultraviolet ray with a
specified wavelength (for example, a wavelength falling within a
range of 300 to 400 nm) can be employed, and as light irradiating
means 112, a black light that irradiates ultraviolet rays for
example, can be used.
If such an electric conductivity measuring cell 91 is constituted,
by irradiating light from light irradiating means 112, titanium
oxide layers 93 provided on the surfaces of the respective
electrodes 94a, 94b, 94c exhibit a photocatalytic activity, and
even when organic substances are contained in a fluid to be
measured flowing in the space 104 for storing a substance to be
measured, the organic substances are decomposed by the
photocatalytic activity. Therefore, even if ion exchange is
performed on the electrode surfaces during the measurement of
electric conductivity, the nonconductive organic substances are
prevented from adhering or being adsorbed onto the electrode
surfaces. As a result, a periodical cleaning of the electric
surfaces is not required any more, and electric conductivity can be
measured stably and accurately at all times without any cleaning.
Further, repeatability of such a high-accuracy measurement can also
be ensured.
Further, if a titanium oxide coating layer is provided on the
surface of glass plate 108 on its side facing the space 104 for
storing a substance to be measured, the adhesion or adsorption of
organic substances to this surface side is also prevented, and
accumulation of the organic substances in the space 104 for storing
a substance to be measured is prevented, thereby maintaining the
high-accuracy measurement.
The structure of the portion of the electric conductivity measuring
cell is not limited to that shown in FIG. 9, and, for example, it
can also be constructed as shown in FIG. 11. In the electric
conductivity measuring cell 121 shown in FIG. 11, three electrodes
122a, 122b, 122c are provided, and for example, the electrode 122a,
122b on both sides are constituted as power supplying electrodes
connected to a power source, and the electrode 122c disposed
between them is constituted as a detection electrode functioning as
a sensor for detecting an electric conductivity. Through holes
123a, 123b, 123c are opened at the central portions of the
respective electrodes 122a, 122b, 122c, and titanium oxide layers
are provided on the inner surfaces of the respective holes 123a,
123b, 123c. Spacers 124a, 124b, 124c, 124d made of a light
transmitting insulation material (for example, 4-fluoride ethylene)
are disposed on both sides of the respective electrodes 122a, 122b,
122c, and the respective electrodes and spacers are stacked
alternately. Through holes 125a, 125b, 125c, 125d are opened also
in the central portions of spacers 124a, 124b, 124c, 124d,
respectively. Support materials 126a, 126b are disposed outside of
spacers 124a, 124d positioned at both sides, and a stacked body
comprising the electrodes 122a, 122b, 122c, and the spacers 124a,
124b, 124c, 124d are sandwiched from both sides by the support
materials. Through holes 127a, 127b are opened also in the central
portions of the respective support materials 126a, 126b, and into
the holes 127a, 127b, one end of a tube 128a for introducing a
fluid to be measured, and one end of a tube 128b for discharging
the fluid are inserted and fixed, respectively.
A flow path of a fluid to be measured is formed by holes 125a,
123a, 125b, 123c, 125c, 123b, 125d connected by stacking the
electrodes 122a, 122b, 122c and the spacers 124a, 124b, 124c, 124d.
A fluid to be measured introduced through tube 128a is discharged
through tube 128b, after flowing inside of this flow path. These
tubes 128a, 128b are composed of a light transmitting material (for
example, 4-fluoride ethylene), and an ultraviolet ray with a
predetermined wavelength is irradiated from black light 129
provided as means for irradiating light. As the ultraviolet ray
irradiated repeats diffusion and reflection in tubes 128a, 128b as
well as transmits the tubes, the ultraviolet ray is guided along
the tubes 128a, 128b, and guided to the inner surfaces formed by
titanium oxide layers in the respective electrodes 122a, 122b, 122c
from the portions of holes 127a, 127b at both sides. Further, as
the respective spacers 124a, 124b, 124c, 124d are also composed of
a light transmitting material, the ultraviolet ray from black light
129 is irradiated to the inner surfaces of electrodes 122a, 122b,
122c after transmitting each spacer while utilizing diffusion and
reflection. Especially, by forming each electrode and spacer to be
relatively thin (for example, the thickness of each electrode is
about 0.2 mm, and the thickness of each spacer is about 1 mm),
because the flow path formed by the respective electrodes and
spacers becomes relatively short, even if a particular light
transmitting material such as an optical fiber is not used, a
sufficient amount of light for measurement is irradiated onto
predetermined electrode surfaces by the light guiding along light
transmitting tubes 58a, 58b as described above, and by the light
guiding through light transmitting spacers 124a, 124b, 124c, 124d.
Therefore, in this embodiment, a simpler and smaller unit can be
constructed.
INDUSTRIAL APPLICATION OF THE INVENTION
In the multiple electric conductivity measuring apparatus according
to the present invention, a micro difference or variation of
electric conductivity between a plurality of measuring points
different in position or time can be determined with a high
reliability, a high accuracy and a high sensitivity. Therefore, the
multiple electric conductivity measuring apparatus according to the
present invention is extremely useful particularly for measurement
of a micro difference or variation of electric conductivity between
a plurality of measuring points in a water treatment system,
thereby obtaining reliable measured data at a high accuracy and a
high sensitivity.
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